Cellular and wireless communication devices have seen explosive growth over the past several years. This growth has been fueled by better communications hardware, larger networks, and more reliable protocols. Today's smartphones include cameras, GPS receivers, Bluetooth® transceivers, and of course the cellular communication capabilities (e.g., LTE, 3G and/or 4G network access) to enable the mobile devices to establish data communication links with the Internet. Smartphones are now very widely deployed in society. Additionally, the components and capabilities in smartphones are now very affordable, enabling the capabilities to be deployed in other types of devices.
Many networks have been deployed to support these wireless devices, and wireless devices may now include more than one network interface to take advantage of multiple available networks. However, wireless devices often have a limited power supply (i.e., battery) and the multiple radio devices needed to simultaneously operate more than one network interface can be a heavy drain on power.
Some modern wireless devices allow two or more network interfaces to share a single receiver/transmitter chain (i.e., the circuitry associated with the radio between the antenna and the modem). For example, a mobile phone may be configured such that two or more SIM (subscriber identity module) cards may share a single transceiver (e.g., dual SIM dual standby “DSDS”). Such a phone allows users to send and receive data on multiple networks using only a single radio.
However, the receiver/transmitter chain in such devices only tunes to a single network at a time, and therefore the two or more network interfaces cannot operate simultaneously. Instead, the mobile device may monitor multiple interfaces in a standby mode by tuning to one network and then to the other network. For example, the radio may connect to a first network and periodically tune-away to other networks on standby to maintain service. In this tune-away procedure, the radio quickly tunes to the standby network for a relatively short time and then tunes back to the first network to continue a voice or data call. This “tune-away” procedure allows the mobile device to monitor for pages (e.g., pages associated with maintaining connections to a network and indicating incoming calls) received on the standby network(s). If a page is received, a user may switch networks if desired or the mobile device may automatically switch networks, such as to answer an incoming telephone call.
The tune-away procedure allows a mobile device to monitor multiple networks but there is a cost. Tuning away to another network typically interrupts transmissions to the first network, because in conventional mobile devices both the receiver and transmitter circuits are tuned to the new network. This can reduce throughput of data transmitted to and from the first network for the mobile device, since the transmitter of the mobile device must pause data transmissions for the duration it is tuned away to the standby network. This may interrupt tracking of the mobile device or synchronization between the first network and the mobile device. This interruption can also delay sending acknowledgements by the mobile device, which in some instanced may cause the network to time out, which wastes energy associated with resending data that was actually received successfully. Also, interruptions can delay sending rate control, flow control, or channel quality feedback. The cost of these issues can add up as a multi-technology mobile device may tune-away frequently.